This invention is directed to molding compositions comprising blends of a polyarylate derived from a dihydric phenol and a dicarboxylic acid, and a polyetherimide. The compositions can also contain thermoplastic polymers compatible with the blends of polyarylate and polyetherimide.
Polyarylates are aromatic polyesters derived from a dihydric phenol, particularly 2,2-bis-(4-hydroxyphenyl)propane (also identified as Bisphenol-A) and an aromatic dicarboxylic acid, particularly mixtures of terephthalic and isophthalic acids.
Polyarylates are high temperature, high performance thermoplastic polymers with a good combination of thermal and mechanical properties. They have a high continuous use temperature of about 130.degree. C., and good unnotched toughness, with a pendulum impact value of greater than 300 ft. lbs./in..sup.3. Additionally, polyarylates have inherent flammability and combustion resistance as well as good weather-ability. The polyarylates have good melt stability at high temperatures and good color retention. They also have good processability which allows them to be molded into a variety of articles.
However, when polyarylates are placed in a solvent environment they readily stress crack so that stress crack resistance of polyarylates is not as high as those of crystalline thermoplastic polymers.
Thus, it is desirable to increase the environmental stress crack resistance of polyarylates to make them more acceptable for use in a solvent environment without essentially effecting the other mechanical properties of the polyarylates.
It has now been unexpectedly found that the addition of a polyetherimide to a polyarylate yields compositions which have significantly improved environmental stress crack resistance. Also, the compositions containing polyetherimide and polyarylate have excellent mechanical compatibility over the entire range and have excellent mechanical properties. Further, addition of the polyarylate to the polyetherimide results in improved impact strength of the polyetherimide.
Additionally, it has been found that when a thermoplastic polymer which is compatible with the blend of polyarylate and polyetherimide is added to said blend, the resulting blends possess an acceptable balance of mechanical properties.